I haven't seen anything on expected battery life but I'd be surprised if it didn't last at least a few years. The key is referred to by Ford as being passive and doesn't actively transmit anything (which would likely be the greatest power drain over time) until it receives a request from one of the three PATS (passive anti-theft system) antennas in the car. This would be at engine start and at some periodic interval afterwards to ensure the key is still in the car, such as when a door is opened.How often should the the key remote battery be replaced. I had my previous VW 5 years and never had to replace but it was the switch blade not smart key.
Yes and no. The keys use the 433 Mhz or 315 Mhz band and when you touch the start button or a door handle the car "pings" the key on a frequency. There are probably 4 antenna in the car, and based on the keys ping responses the car knows the physical location of the key. If it's outside on the right, and that door handle was used it unlocks, the same for being on the left with the left door handle. The start button should work if the key is inside the car. The battery does help power that transmitter (that responds to the ping) but it only does so in the form of amplification (as in the op-amp needs the battery). Without the battery the range on the RF is VERY VERY small, hence the slot in the column. There is typically a coil around those slots and with the coil you can detect the miniscule RF range that the unamplified key has.RFID tech is apparently being used here. In which the transmitter in the vehicle emits RF radiation (no not the scary stuff) that excites the RFID receiver in the fob. The car is wirelessly powering the fob sort of like that cordless iPhone charger you all saw a few years ago, although at a much smaller power level.
I assume the buttons are the only thing that uses the battery.
I did this, I had the keys in a pair of jeans in my bag I was holding and didn't realize they weren't in my pocket. I opened the hatch, put my stuff in and closed it.Just today, I forgot my fob was in my gym bag. I threw the bag in the trunk (which I opened by just using the handle and the RF signal generated from the FOB in the bag), this was mistake number one. I thought for a moment where my fob was...in my bag. But assumed since the fob was now in the car, I would still be able to open the doors. Mistake number two. I went back to the trunk, and you guessed it, mistake number three, it wouldn't open. So there I was... locked out of my ST. I honestly thought it couldn't happen with the FOB physically in the car. :S
The learning point: Leaving the FOB in the front seats..OK. Back seats>>>I don't know. Trunk>>> No Dice.
I have also had issues where I am in the car, someone gets out, I wait for them, make sure the lock button is on Unlock and I still have to open my door first for them to open a door or the trunk..? Anyone else experience this?